#include <nmea.h>

// create a GPS data connection to GPRMC sentence type
NMEA gps(GPRMC);

void setup() {
  Serial1.begin(4800);
  pinMode(8, OUTPUT);
}

void loop() {
  if (Serial1.available() > 0 ) {
    // read incoming character from GPS
    char c = Serial1.read();

    // check if the character completes a valid GPS sentence
    if (gps.decode(c)) {
      // check if GPS positioning was active
      if (gps.gprmc_status() == 'A') {
        // read speed in kilometers-per-hour and set led accordingly
        if (gps.gprmc_speed(KMPH) > 50.0) {
          digitalWrite(8, HIGH);
        } else {
          digitalWrite(8, LOW);
        }
      }
    }
  }
}